A Radio Signal That Refuses to Fade express

Original: "VLASS Discovery of a Luminous Galactic Radio Transient Evolving on Decade Timescales"
arXiv:2608.21320v1 · 2026-08-21 · CC BY 4.0 · 2 min
Astronomers have found a radio source in our Galaxy that flares, fades, and blazes again — unlike anything we've seen.

Radio telescopes listen to the sky like sensitive ears: they catch the whispers of distant explosions, the hum of galaxies, the crackle of pulsars. But sometimes they pick up a sound that isn't in the catalogs. In 2003, such a sound emerged in the constellation Aquila — a spot in the sky that had been quiet until it suddenly began to speak.

The source was named VT J1906+0849. It lies nearly in the plane of the Milky Way, amid dense clouds of gas and dust. At first, it brightened: by 2014, its radio brightness had tripled compared to the first measurement. Then it began to fade. The story seemed over. But in late 2025, it flared again, like a campfire fed with fresh kindling.

So what is it? Given its distance (at least 15,000 light-years from us) the source is extremely powerful. To shine this brightly in radio, matter must be continuously falling onto a compact object, either a black hole or a neutron star. But here's the puzzle: the Swift X-ray telescope saw no bright X-ray emission, which usually accompanies such "feeding." And the radio waves vary in ways unlike typical black hole binary systems.

The radio spectrum suggests the emission arises in a dense clump where electrons spiral along magnetic field lines. Yet the clump itself barely expands — over five years of observations, its size remained constant, even as brightness and color changed. This happens when a jet is squeezed on all sides, like a stream of water clenched in a fist.

In the infrared spectrum, astronomers found a single broad hydrogen line. Its center stays fixed, but its width and brightness vary. This looks like a steady wind blowing from the object at about 2000 kilometers per second — toward us.

None of this fits the usual patterns. The closest behavioral relative is the famous microquasar SS 433, which ejects narrow jets at a quarter of the speed of light. But VT J1906+0849 is younger and fainter in X-rays. Perhaps its jet hasn't yet punched through a dense cocoon of gas that slows it down and prevents expansion. The jet crashes against the cocoon's walls like water against rock, generating radio waves — while the same dense material quenches X-ray emission.

This scenario explains the flares, the "frozen" size, and the strange wind. If correct, we are witnessing a rare moment: the birth of a microquasar, when a black hole is just beginning to carve its path through matter that has fallen onto it from a companion star.

The wind speed at VT J1906+0849 is 2000 km/s—200 times faster than a bullet and 6 times faster than lightning in a thunderstorm.

A similar plot appears in the movie Interstellar: the accretion disk around the black hole Gargantua shines brightly, while powerful jets shoot out, visible from afar.

Scientists
Bernhard RiemannJoseph WeberKarl SchwarzschildKip ThorneRainer WeissAlbert Einstein
Concepts
vla meerkat radio wave rotating radio transient jwst red sources fast radio burst